1. Technical Field
The present invention relates to printing apparatuses and printing methods.
2. Related Art
Such a printer is widely known that includes a printing head called a line head in which a row of nozzles whose length is approximately equal to the width of a print medium is provided, and serves as an ink jet printer configured to perform printing by discharging ink through a plurality of nozzles. There is provided a line head which is constructed by serially connecting a plurality of heads each of which is shorter than the entire length of the line head in one direction (longitudinal direction of the line head). In the case where the above configuration is employed, the heads are connected so that an end portion of one head and an end portion of another head are intentionally overlapped each other in the longitudinal direction of the line head while taking into consideration an attachment error at a connecting portion of the heads.
A density of nozzles at the connecting portion is locally higher than that at another portion other than the connecting portion in the line head. Accordingly, in order to prevent deterioration in image quality when discharged results by the heads overlap with each other at the positions corresponding to the connecting portion on a print medium, it has been carried out to control the amount of ink discharged through the nozzle in the vicinity of the end portion of each head to decrease in a gradational manner as the position of the nozzle is closer to the end portion of the head, or the like.
Meanwhile, in an ink jet printer, if such a state continues that ink is not discharged through the nozzles, moisture of the ink evaporates through the openings of the nozzles so that viscosity of the ink increases in some case. If the viscosity of ink increases, the nozzles are clogged and so on, consequently ink discharge operation becomes unstable in some case. In order to prevent the occurrence of such problem, it is preferable that what is called “flushing” be performed to prevent or solve the clogging of the nozzles. Flushing is a process in which ink is forcibly discharged through the nozzles.
As a related technique, well-known is an image forming apparatus that includes a recording head (line head) in which a plurality of heads each having a plurality of nozzles arranged therein for discharging droplets are aligned in a staggered manner in a nozzle arrangement direction, and in which the nozzles at the end portions of the heads overlap each other in the nozzle arrangement direction; the image forming apparatus performs a non-printing discharge (flushing) of droplets through the overlapped nozzles in the heads onto a transport belt configured to transport paper, and performs another non-printing discharge of droplets onto paper through the nozzles which are not concerned with the non-printing discharge onto the transport belt (see JP-A-2010-137388). Note that the non-printing discharge does not contribute to image formation.
Since flushing is performed to prevent the nozzles from being clogged and so on, each nozzle need perform a certain amount of flushing whether the nozzle belongs to the connecting portion or not. Accordingly, in the case where the above-described control operation is performed on the flushing in which the amount of ink discharge through the nozzle in the vicinity of the end portion of the head is decreased in a gradational manner as the position of the nozzle is closer to the end portion of the head, such a risk can arise that there exist some nozzles through which necessary and sufficient flushing is not performed.
Meanwhile, in the case where flushing is performed through the nozzles in a uniformed manner whether the nozzles belong to the connecting portion or not, when the flushing results by the heads that belong to the connecting portion overlap with each other on a print medium, stripe-shaped unevenness or the like is visually recognized in comparison with other area on the print medium. This can lead to a risk of occurrence of deterioration in image quality. Further, in JP-A-2010-137388, since flushing is performed through the overlapped nozzles (the nozzles belonging to the connecting portion) onto the transport belt, throughput of the printing is lowered. In addition, it has been needed to surely prevent the deterioration in image quality, which can occur due to the presence of the connecting portions.